Neutronenkleinwinkelstreuung an der Legierung Al-Zn oberhalb des kritischen Punktes

Schwahn, D.

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FZJ-2018-00951

Neutronenkleinwinkelstreuung an der Legierung Al-Zn oberhalb des kritischen Punktes

Schwahn, D. (Corresponding author)FZJ*

1976
Kernforschungsanlage Jülich, Verlag Jülich

Jülich : Kernforschungsanlage Jülich, Verlag, Berichte der Kernforschungsanlage Jülich 1379, 76 p. (1976)

Please use a persistent id in citations: http://hdl.handle.net/2128/16901

Report No.: Juel-1379

Abstract: The coherent composition fluctuation in the system Al-Zn were measured by neutron small angle scattering in the temperature range between 435 and 324 $^\circ$C. No critical scattering could be detected at the incoherent critical point (T$_{k}$ = 351.5 $^\circ$ C, c$_{k}$ = 39.5 at.% Zn in Al). In the temperature interval from435 to 324$^\circ$ C the intensity of the scattered neutrons increases continuously in the measured [...]-region. The scattering curves below T = 324$^\circ$ C differ from the others by their high intensity for small [...]- and their strong decreases to larger [...]-values. These results agree with Cahn's theory which predicts a decrease of the real critical point due to the elastic energy built up by the composition fluctuations. The theoretical estimation for the system Al-Zn gives a shift of $\Delta$T = 25 degree. The strong increase of the intensity below T - 324$^\circ$ C is due to the boundary of the unstable region of the phasediagram. Moreover one could follow up the growth of the incoherent precipitates in the metastable region of the phasediagram, and the incoherent critical point could be determined as the highest point of the two-phase region. Experimentally determined and theoretieally calculated parameters were compared which describe the scattering law completely. These parameters are the scattering cross section for forward scattering and the square of the reciprocal correlation length. The comparison shows that Cahn's model also describes quant itatively weIl the coherent composition fluctuations in the system Al-Zn.

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